The invention relates to a hydraulic accumulator, and particularly relates to a hydraulic accumulator including a self-seal stay with a weakened portion.
An automobile's brake circuit or the like has a hydraulic circuit, which employs a hydraulic accumulator for temporarily storing fluid increased in pressure. The hydraulic accumulator includes a gas chamber in which a gas of a high pressure is sealed, and a fluid chamber in which a hydraulic fluid (hydraulic oil) is introduced. The gas chamber and the fluid chamber are arranged opposite to each other relative to an expandable and contractable bellows. Expanding and contracting of the bellows makes the pressure of the gas chamber and the pressure of the fluid chamber balance with each other, which prevents pulsation of the hydraulic circuit to regulate it to an appropriate hydraulic pressure.
In a conventional hydraulic accumulator, for example, if an automobile is subjected to a fire or the like and placed under a high temperature or high pressure circumstance for a long time, the inner pressure of the gas chamber in the hydraulic accumulator can excessively increase. For this reason, the hydraulic accumulator includes a relief means which releases the inner pressure of the gas chamber when it is placed under such an abnormal situation. Refer to patent document 1: Patent Application Publication Laid-open No. 2003-172301 and patent document 2: Patent Application Publication Laid-open No. 2012-237415.
The patent document 1 describes a hydraulic accumulator provided with a weakened portion which serves as a relief means for releasing inner pressure of the gas chamber and is formed by reducing a thickness of the sidewall of the stay disposed in the fluid chamber (refer to paragraph [0017] and FIG. 1). In the hydraulic chamber, when the inner pressure of the gas chamber excessively increases, the excessively increased inner pressure of the gas chamber causes the bellows to be pressed and the inner pressure of the fluid chamber to be increased, thereby breaking the weakened portion.
Then, breaking the weakened portion makes hydraulic fluid of a high pressure discharged from the fluid chamber to decrease the pressure in the fluid chamber. The excessively increased inner pressure of the gas chamber causes the bellows to be intentionally broken to release the inner pressure of the gas chamber from the communication hole formed in the head portion of the stay.
The patent document 2 describes a hydraulic accumulator formed with a shapedly weakened portion, which serves as a relief means for releasing then inner pressure of the gas chamber and is simultaneously formed during press forming of the metal-made stay. This shapedly weakened portion causes the metal-made stay to be buckled to further securely release liquid and gas in the shell (refer to claims 1 and 2, paragraph [0009], and FIGS. 2 to 8).
In the hydraulic accumulator described in the patent document 1, however, when the weakened portion is broken to release the inner pressure of the gas chamber, breaking suddenly occurs. This causes explosive sound at the breaking, resulting in sense of anxiety. When the weakened portion is broken, the inner pressure is released excessively instantaneously. This makes it difficult to regulate a relief pressure for releasing pressure in the gas chamber. If the hydraulic accumulator tries to be downsized, the stay of a low height enhances its rigidity, which makes it difficult to break the stay.
In the hydraulic accumulator described in the patent document 2, if formation accuracy and thickness accuracy try to be strictly ensured, the number of steps for working a mold and the number of adjustments increase, while it is difficult to regulate relief pressure for releasing the pressure in the gas chamber.
The first object of the invention is to reduce the number of steps for fabricating a hydraulic accumulator with a simple construction.
The second object of the invention is to facilitate regulating a relief pressure for releasing pressure in a gas chamber.
The third object of the invention is to release a high pressure gas in a gas chamber at a proper timing.
The fourth object of the invention is to properly control a relief pressure of the high-pressure gas.